RESUMO
Elongation of the head-to-tail body axis by convergent extension is a conserved developmental process throughout metazoans. In Drosophila, patterns of transcription factor expression provide spatial cues that induce systematically oriented cell movements and promote tissue elongation. However, the mechanisms by which patterned transcriptional inputs control cell polarity and behaviour have long been elusive. We demonstrate that three Toll family receptors, Toll-2, Toll-6 and Toll-8, are expressed in overlapping transverse stripes along the anterior-posterior axis and act in combination to direct planar polarity and polarized cell rearrangements during convergent extension. Simultaneous disruption of all three receptors strongly reduces actomyosin-driven junctional remodelling and axis elongation, and an ectopic stripe of Toll receptor expression is sufficient to induce planar polarized actomyosin contractility. These results demonstrate that tissue-level patterns of Toll receptor expression provide spatial signals that link positional information from the anterior-posterior patterning system to the essential cell behaviours that drive convergent extension.
Assuntos
Padronização Corporal/genética , Proteínas de Drosophila/genética , Proteínas de Drosophila/metabolismo , Drosophila melanogaster/embriologia , Receptores Toll-Like/genética , Receptores Toll-Like/metabolismo , Animais , Polaridade Celular/genética , Proteínas de Ligação a DNA/genética , Proteínas de Ligação a DNA/metabolismo , Drosophila melanogaster/citologia , Drosophila melanogaster/genética , Embrião não Mamífero , Regulação da Expressão Gênica no Desenvolvimento , Proteínas de Homeodomínio/genética , Proteínas de Homeodomínio/metabolismo , Miosina Tipo II/metabolismo , Proteínas Nucleares/genética , Proteínas Nucleares/metabolismo , Transporte Proteico , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismoRESUMO
Cornelia de Lange syndrome (CdLS) is a multisystem genetic disorder with distinct facies, growth failure, intellectual disability, distal limb anomalies, gastrointestinal and neurological disease. Mutations in NIPBL, encoding a cohesin regulatory protein, account for >80% of cases with typical facies. Mutations in the core cohesin complex proteins, encoded by the SMC1A, SMC3 and RAD21 genes, together account for â¼5% of subjects, often with atypical CdLS features. Recently, we identified mutations in the X-linked gene HDAC8 as the cause of a small number of CdLS cases. Here, we report a cohort of 38 individuals with an emerging spectrum of features caused by HDAC8 mutations. For several individuals, the diagnosis of CdLS was not considered prior to genomic testing. Most mutations identified are missense and de novo. Many cases are heterozygous females, each with marked skewing of X-inactivation in peripheral blood DNA. We also identified eight hemizygous males who are more severely affected. The craniofacial appearance caused by HDAC8 mutations overlaps that of typical CdLS but often displays delayed anterior fontanelle closure, ocular hypertelorism, hooding of the eyelids, a broader nose and dental anomalies, which may be useful discriminating features. HDAC8 encodes the lysine deacetylase for the cohesin subunit SMC3 and analysis of the functional consequences of the missense mutations indicates that all cause a loss of enzymatic function. These data demonstrate that loss-of-function mutations in HDAC8 cause a range of overlapping human developmental phenotypes, including a phenotypically distinct subgroup of CdLS.
Assuntos
Fontanelas Cranianas/anormalidades , Síndrome de Cornélia de Lange/enzimologia , Anormalidades do Olho/enzimologia , Genes Ligados ao Cromossomo X , Histona Desacetilases/genética , Hipertelorismo/enzimologia , Proteínas Repressoras/genética , Sequência de Aminoácidos , Criança , Pré-Escolar , Estudos de Coortes , Fontanelas Cranianas/enzimologia , Síndrome de Cornélia de Lange/genética , Anormalidades do Olho/genética , Feminino , Histona Desacetilases/química , Histona Desacetilases/metabolismo , Humanos , Hipertelorismo/genética , Lactente , Masculino , Dados de Sequência Molecular , Mutação de Sentido Incorreto , Fenótipo , Proteínas Repressoras/química , Proteínas Repressoras/metabolismo , Alinhamento de SequênciaRESUMO
Whole-body regeneration requires the ability to produce the full repertoire of adult cell types. The planarian Schmidtea mediterranea contains over 125 cell types, which can be regenerated from a stem cell population called neoblasts. Neoblast fate choice can be regulated by the expression of fate-specific transcription factors (FSTFs). How fate choices are made and distributed across neoblasts versus their post-mitotic progeny remains unclear. We used single-cell RNA sequencing to systematically map fate choices made in S/G2/M neoblasts and, separately, in their post-mitotic progeny that serve as progenitors for all adult cell types. We defined transcription factor expression signatures associated with all detected fates, identifying numerous new progenitor classes and FSTFs that regulate them. Our work generates an atlas of stem cell fates with associated transcription factor signatures for most cell types in a complete adult organism.
Assuntos
Planárias , Fatores de Transcrição , Animais , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismo , Planárias/metabolismo , Células-Tronco/metabolismo , Diferenciação Celular , Regulação da Expressão GênicaRESUMO
Neuronal circuits damaged or lost after injury can be regenerated in some adult organisms, but the mechanisms enabling this process are largely unknown. We used the planarian Schmidtea mediterranea to study visual system regeneration after injury. We identify a rare population of muscle cells tightly associated with photoreceptor axons at stereotyped positions in both uninjured and regenerating animals. Together with a neuronal population, these cells promote de novo assembly of the visual system in diverse injury and eye transplantation contexts. These muscle guidepost-like cells are specified independently of eyes, and their position is defined by an extrinsic array of positional information cues. These findings provide a mechanism, involving adult formation of guidepost-like cells typically observed in embryos, for axon pattern restoration in regeneration.
Assuntos
Axônios/fisiologia , Olho/citologia , Músculos/fisiologia , Fenômenos Fisiológicos Oculares , Células Fotorreceptoras de Invertebrados/fisiologia , Planárias/fisiologia , Regeneração , AnimaisRESUMO
The transcriptome of a cell dictates its unique cell type biology. We used single-cell RNA sequencing to determine the transcriptomes for essentially every cell type of a complete animal: the regenerative planarian Schmidtea mediterranea. Planarians contain a diverse array of cell types, possess lineage progenitors for differentiated cells (including pluripotent stem cells), and constitutively express positional information, making them ideal for this undertaking. We generated data for 66,783 cells, defining transcriptomes for known and many previously unknown planarian cell types and for putative transition states between stem and differentiated cells. We also uncovered regionally expressed genes in muscle, which harbors positional information. Identifying the transcriptomes for potentially all cell types for many organisms should be readily attainable and represents a powerful approach to metazoan biology.
Assuntos
Atlas como Assunto , Células/classificação , Perfilação da Expressão Gênica/métodos , Planárias/citologia , Análise de Sequência de RNA/métodos , Análise de Célula Única/métodos , Transcriptoma , Animais , Linhagem da Célula/genética , Células/citologia , Células/metabolismo , Células-Tronco/metabolismoRESUMO
Planarians are flatworms capable of regenerating any missing body part in a process requiring stem cells and positional information. Muscle is a major source of planarian positional information and consists of several types of fibers with distinct regulatory roles in regeneration. The transcriptional regulatory programs used to specify different muscle fibers are poorly characterized. Using single-cell RNA sequencing, we define the transcriptomes of planarian dorsal-ventral muscle (DVM), intestinal muscle (IM), and pharynx muscle. This analysis identifies foxF-1, which encodes a broadly conserved Fox-family transcription factor, as a master transcriptional regulator of all non-body wall muscle. The transcription factors encoded by nk4 and gata4/5/6-2 specify two different subsets of DVM, lateral and medial, respectively, whereas gata4/5/6-3 specifies IM. These muscle types all express planarian patterning genes. Both lateral and medial DVM are required for medial-lateral patterning in regeneration, whereas medial DVM and IM have a role in maintaining and regenerating intestine morphology. In addition to the role in muscle, foxF-1 is required for the specification of multiple cell types with transcriptome similarities, including high expression levels of cathepsin genes. These cells include pigment cells, glia, and several other cells with unknown function. cathepsin+ cells phagocytose E. coli, suggesting these are phagocytic cells. In conclusion, we describe a regulatory program for planarian muscle cell subsets and phagocytic cells, both driven by foxF-1. FoxF proteins specify different mesoderm-derived tissues in other organisms, suggesting that FoxF regulates formation of an ancient and broadly conserved subset of mesoderm derivatives in the Bilateria.
Assuntos
Padronização Corporal/genética , Regulação da Expressão Gênica no Desenvolvimento , Proteínas de Helminto/genética , Planárias/crescimento & desenvolvimento , Planárias/genética , Fatores de Transcrição/genética , Animais , Proteínas de Helminto/metabolismo , Desenvolvimento Muscular/genética , Fagócitos/metabolismo , Fatores de Transcrição/metabolismo , TranscriptomaRESUMO
Cornelia de Lange syndrome (CdLS; or Brachmann-de Lange syndrome) is a dominantly inherited congenital malformation disorder with features that include characteristic facies, cognitive delays, growth retardation and limb anomalies. Mutations in nearly 60% of CdLS patients have been identified in NIPBL, which encodes a regulator of the sister chromatid cohesion complex. NIPBL, also known as delangin, is a homolog of yeast and amphibian Scc2 and C. elegans PQN-85. Although the exact mechanism of NIPBL function in sister chromatid cohesion is unclear, in vivo yeast and C. elegans experiments and in vitro vertebrate cell experiments have demonstrated that NIPBL/Scc2 functionally interacts with the MAU2/Scc4 protein to initiate loading of cohesin onto chromatin. To test the significance of this model in the clinical setting of CdLS, we fine-mapped the NIBPL-MAU2 interaction domain and tested the functional significance of missense mutations and variants in NIPBL and MAU2 identified in these minimal domains in a cohort of patients with CdLS. We demonstrate that specific novel mutations at the N-terminus of the MAU2-interacting domain of NIBPL result in markedly reduced MAU2 binding, although we appreciate no consistent clinical difference in the small group of patients with these mutations. These data suggest that factors in addition to MAU2 are essential in determining the clinical features and severity of CdLS.